Electric heating plate



ELECTRIC HEATING PLATE Filed .Sept. 15, 1931 INVENTOR Gas 1 Ca/ze ATTORN EY Patented Feb. 19, 1935 UNITED STATES PATENT OFFICE ELECTRIC HEATING PLATE Application September 15, 1931, Serial No. 562,934

'6 Claims.

My invention relates to a novel form of electric heating plate of the type used in connection with electric cooking stoves, hot plates and the like, in combination with a supporting means which also forms a means through which electrical current is supplied.

Electric heating plates in common use have certain undesirable qualities which have always been annoying to the housekeeper. Among these undesirable qualities is the accumulation of food particles, dust and other foreign matter in and around the grid resistor or heating coil, which have to be cleaned out periodically and each attempt to clean same is a slow and tedious operation. The one effective method of performing this cleaning operation is to entirely remove the plate which supports the grid resistor, but this is not a convenient method for the average person since the electrical connections have to be removed before the plate can be taken' out, and such removal by an unskilled person might prove hazardous if the current supply is not disconnected.

It is one object of my invention toconstruct an electric heating plate which is easily accessible toremove for cleaning and which may be replaced without manipulating any contacts, thereby protecting the person removing same from any danger of electrical shock as well as making it a 30 simple task to keep grid resistors clean.

Another feature of my invention includes a method of insulating to prevent dissipation of heat in any but the desired direction for which it was intended to flow.

Other features include the mounting ofcontact members to provide adequate electrical connection when engagement is made between thev grid plate and current supply contacts, and the arrangement of the grid plate within its support to assure proper alignment of said contacts.

By the arrangement of parts in my heating plate I provide a refractory plate, in which is mounted a preferably low potential grid resistor having contact members attached to the terminals of same and exposed below said refractory plate. The ends of the resistor contacts are angularly disposed and are adapted to engage similar angularly disposed surfaces of current supply contacts mounted within a stove top or other suitable support upon which the plate is placed. The current supply contacts provide two points of support. for the heating plate and actually carry most of the weight of same, thus providing a wedging contact between the said angularly disposed contact surfaces with suflicient pressure to assure an adequate electrical connection. A third point of support for the heating plate is so designed to permit the placement of said heating plate in only one possible position in which the resistor and current supply contacts are in exact alignment.

The preferred arrangement of mounting is to have the heating plate set in a pocket formed in the stove top, then insulating the portion surrounding said pocket in such a manner as to provide a combined form of insulation comprising an air chamber backed by a packed insulation and another air chamber surrounding the latter.

The best form of apparatus at present known to me is illustrated in the accompanying drawing, in which,

Fig. 1 is a plan view of the heating plate mounted upon a stove top. 4

Fig. 2 is a cross section through the heating plate and insulating portions taken on the lines 2-2 of Fig. 1, and

Fig. 3 is a cross section taken on the lines 3 3 of Fig. 1 showing a contact mounting.

Throughout the drawing like reference characters represent like parts.

The heating plate designated generally by the reference letter P, comprises a novel form of low potential grid resistor 18 mounted within a cavity 22 in a refractory plate 10, and is adapted to be placed upon a stove top 16 as indicated in the drawing, or any other suitable support.

Three heat insulating compartments are arranged below and around the heating plate P. The first of these is an air chamber 17 beneath the grid plate 10, second, a packed insulated compartment 40 surrounding the lower portion of said chamber 1'7, and third, another air chamber 50 surrounding the lower portion of the insulated compartment 40. The first air chamber 1'1 is the space within a dished portion 14 formed in the sheet metal stove top 16, into which the heating plate P is partly submerged. A metallic sheet 42 is formed to fit over an insulating packing 41 to provide the second insulating compartment, and a metallic sheet 46, shaped similar to the sheet 42, is placed over said sheet 42 in spaced relation and welded thereto, thus leaving an air chamber within it. The sheets 42 and 46 may be welded to the stove top sheet 16 along their flanged edges 4448 or secured in any other convenient way. While I have shown the insulating portions in the order of air space, insulated packing and air space, the same may be varied as desired. 1

The grid resistor 18 is preferably made of a low potential resistance wire shaped in serpentine fashion to form several equally spaced continuous parallel wires as illustrated in Fig. 1. Terminal studs are welded to the resistor wire ends, said studs having-threaded shanks 24 which project through holes 25 in the refractory plate 10 after the resistor is placed in the cavity 22. A central rib 23 may be formed within the cavity 22 of therefractory plate to provide an intermediate spacing member for the resistor 18 and to support cooking utensils. Two contact straps 26 placed over the ends of the projecting shanks 24 are secured by means of nuts 28, the forward or contact ends 30 of which straps are bent upward at a suitable angle, and project into a recessed portion 32 in the lower surface of the grid plate as shown in Fig. 3..

The refractory plate 10 with its grid 18 and terminal strap connections 26, forms the complete heating unit, which is adapted to be placed in such position as to have its strap connections 26 seat upon the beveled heads 34 of two current supply terminal contacts, designated generally by the arrow 33, which project upward from within the dished portion 14 of the stove top. The outer surfaces of the angularly disposed portions of the contact straps 26, engage beveled faces 35 of said supply terminal contacts 33 and when placed in this contact position, most of the weight of the plate 10 is supported by the said contact members 33.

By disposingtthe contact surfaces of the beveled head 35 and contact strap 30 at an angle, a wedging action is obtained which provides a substantial contact pressure to assure an adequate electrical connection. This contact pressure may be altered by changing the angle of the bent end 80 of the contact strap 26 and bevel 35 on the head 34, a greater pressure resulting when the line of contact between these approaches the vertical.

Shanks 52, projecting below the heads 34 of the contact members, are mounted within insulating bushings 54. Said bushings 54are suspended by their flanges 53 from the cover of the stove top 16, the lower reduced portions projecting through the openings 56, 5'1 and 58 in the stove top and sheets 42 and 46 respectively of the insulating members. Two sleeves 66 around each bushing 54 are disposed one between the stove top 16 and sheet 42 and the other between sheets 42 and 46.

An insulating collar 64 is placed over the lower end of the bushing 54 projecting beyond the bottom of the heat insulating structure, and a washer is placed over the lower end of the shank 52, one face of said washer engaging the lower surface of the insulated collar 64. A nut 62 is drawn up over the threaded lower end of the shank 52, engaging a current supply con- Cnector strap 59, placed between the said nut 62 and the washer 60, the tightening of which nut 62 not only provides a tight connection for the strap 59, but also draws the flange '53 of the bushing54andtheinsulatingcollar64toward each other so that the stove top 16, sheet 46 and sleeves 66 therebetween, are clamped together,

, th n providing a rigid mounting for the supply contact members i 33, as clearly indicated in 1'18. 3.

The means for controlling the alignment of the resistor plate and current supply contacts when placing the heating pad in position, comprises a flattened edge-12 on the grid plate 10 whichisadaptedtorcsisterwithasimilatshaped portion 15, formed within the wall of the dished opening 14 in the stove top. A ledge 36 is provided which forms a third point of support for the heating plate as shown in Figs. 1 and 2. In order to facilitate the removal ofthe heating plate, a thumb notch 68 is provided in the refractory plate 10, opposite the flattened edge 12. The two electrical contact and support members 34, 34, being located near the lefthand edge of the plate 10 (looking at Figs. 1 and 2) and the third point of plate support afforded by the surfaces 12, 15 and 36 being located at the right hand edge of said plate, 1. e. opposite that along which a straight line connecting 34, 34, would extend a three point triangular based supporting system for the plate is thereby formed, two of the three sets of supporting contacts being electrical. Thus the weight of the heating plate, and of anything resting on it, serves to continuously force a close contact between the current conducting surfaces of 30 and 34. If these contact surfaces are inclined as shown at an acute angle to the plane of the upper surface of the heating plate, a wedging action is produced by gravity between said contact surfaces which further heightens the current conducting efficiency of the circuit connections. Also this produces a side wiping action between the contact surfaces every time the plate is removed or replaced, which wiping action helps to keep said contact surfaces clean.

The non-electrical support afforded at the third point by the plate surface 12, and base surfaces 15 and 36 serves as a hinge about which the resistor plate may be swung when it is being removed or replaced to rest on 34, 34. Obviously other forms of hinge or other supports could be substituted for this particular construction shown.

It is thus obvious from the foregoing description that an improved form of electrical heating plate has been developed which in addition to the novel features referred to, is of very rugged construction comprising very few parts, which will minimize the original cost of manufacture and assembly as well asth'e cost of replacement or repair. Various changes can be made in the details of construction hereshown and described, as forming one embodiment of my invention. any such modifications still being within the scope of the invention here claimed if the principles of operation and results above explained are stantiallypreserved.

Having described my invention, I claim:

1. In an electrical heating apparatus the combinationofasupportingbasehavingarecessof considerable area in its upper surface, two spaced-apart fixed electrical contact members set inthesaidreceasatonesidethereofandto which a supply circuit may be connected, a grid plate of insulating material having substantially the same exterior outlines as said recess. a grid resistor set in the upper surface ofsaid plate and terminal contacts for said resistor located on the under side thereof in position such that whentheplateisnestedin saidrecessoneterminalcontactwillbearononeofthefirstmentioned fixed contacts and the other terminal contact on the other fixed contact, said recess 'insaidsupportingbasehavingaledgeonits periphery remote from said fixed contacts, and

onwhichoneedgeoftheplaterestswhennested insaidrec'ess,asectionoftheedgeportionof said plate nearest said contacts being oflset slightlyfromtheadjacentedgeoftherecessin said'supportingbase;wherebyathreepointsupport for said plate is provided and said plate may be easily removed by the insertion of a finger in the space left by such offsetting and the plate thereby swung upward on said ledge as a hinge.

2. A- combination such as defined in claim 1 in which said stationary contacts have their surfaces facing said ledge inclined upwardly and away therefrom, and in which the terminal contacts on said plate have their surfaces adjacent said fixed contacts similarly inclined; whereby a wedging contact is produced by the weight of said plate when in operative position.

3. A combination such as defined in claim 1 in which said stationary contacts have their surfaces facing said ledge inclined upwardly and away therefrom, and in which the terminal contacts on said plate have their surfaces adjacent said fixed contacts similarly inclined, the side wall of said recess extending upward from said ledge, and the cooperating surface of the edge of said plate, being hoth upwardly inclined away from said contacts; whereby a wedging contact is produced at all points of support by the weight of said plate when in operative position.

4. A combination such as defined in claim 1 in which said recess and said plate are both substantially circular in exterior outline except along said ledge, at which portions the said outlines are straight, and parallel one to another.

5. In an electric stove the combination, with a supporting base, of a removable grid plate having two electrical contact members spaced apart on its under surface near one edge thereof, and said base having two cooperating contact members set in its upper surface, each of said plate contacts having a plate-supporting bearing on its cooperating base contact when the plate is in position, said plate and base being also provided with a third pair of cooperating, non-e1ectrical supporting elements located under the plate edge at a point opposite that along which a straight line connecting the two pairs of electrical contacts extends; whereby a three point support for said plate is provided, at two of which points electrical contact is established, each pair of said electrical contact surfaces being inclined in a plane forming an angle of less than 90 degrees with the plane of the upper surface of said plate; whereby a wedging electrical contact is produced when said plate is allowed to rest thereon.

6. In an electric stove the combination of a base provided with two fixed electrical contact members having their upper surfaces inclined to the horizontal plane, and a heating plate carrying a resistor, the terminals of which are connected to contact members located on the under side thereof, adapted to register with said fixed contacts, and located directly over said fixed contact members when the plate is' in operative position, said contact members having their under surfaces similarly inclined, together with means for preventing horizontal displacement of said plate when it is in position to cause said pairs of contacts to mutually engage by its weight; whereby a wedging electrical contact is produced between said two sets of contact members which support a relatively large portion of the weight of the plate.

GUS L. COLBIE. 

